1. Field of the Invention
The invention relates to an apparatus for gaining pinbone-free fillets of fish conveyed tail first along a conveying path extending along a series of processing tools arranged on either side of said path, the apparatus comprising belly and back filleting tools for cutting free the belly and back spokes, rib severing tools for releasing the fillets from the ribs, severing tools for completely severing the fillets from the sides of the spinal column, and pinbone tools arranged between the belly and back filleting tools, on the one hand, and the rib severing tools, on the other, and being movable under control into the path of the fish during the passage of the belly cavity, said pinbone tools each comprising two spaced circular knives, driven to rotate around a common shaft, for making incisions extending substantially normal to the plane of symmetry of the fish below and above the pinbones essentially up to the ribs and the lateral vertebral appendages, respectively.
2 Prior Art
U.S. Pat. No. 3,570,048 discloses a method and an apparatus which are characterized in that prior to making the first filleting cuts, the pinbones (also termed meat bones in some countries) are cut free by two cuts each, made on either side of the fish in the vicinity of the abdominal cavity.
This method did not prove successful, because there was still a need to trim the fillets manually by removing the meat strip containing the pinbones still connected to the fillets at the end thereof. Thus, this method was not satisfactory, particularly with regard to the attainable rationalization effect. Moreover, it was found that particularly in the case of soft fish and due to the necessary external guidance of the fish during the making of the pinbone cuts, which results in deformation, an economical pinbone cut was only possible when accompanied by an increasing risk of meat bone residues remaining in the fillets.
Therefore, other methods have been developed and are directed at achieving the sought bone freedom of the fillets by removing the belly flaps, including the pinbone strips therein.
Such a method is disclosed in German Pat. No. 24 60 447. After making the belly and back filleting cuts, incisions are made above the pinbone strip, and the fillets are severed from the flanks of the spine and finally cut free by crosscuts made outwardly from the belly filleting cuts in the vicinity of the abdominal cavity end. This is followed by the separation of the belly flaps, attached to the bone structure and including the pinbone row, from the ribs and lateral vertebral appendages.
Apart from a considerable expenditure on guidance and additional conveying means, this method also leads to a quality-reducing stressing of the fillets. However, the method-based stipulation of a boneless fillet without any belly flaps is disadvantageous, because, as part of the fillets, said flaps increase their selling price, whereas the separately obtained flaps can only be utilized as fish farce.